# Troubleshooting of Twin‑Screw Pumps
In practical applications, in addition to common basic problems such as insufficient flow, unstable pressure, and seal leakage, twin‑screw pumps may also encounter some easily overlooked failures and operating condition adaptation issues. The following is a detailed classification and solutions:
## I. Mechanical Transmission and Bearing‑Related Problems
### Bearing Overheating and Seizure
**Causes**:
- Incorrect lubricating oil grade (too high / too low viscosity) or insufficient oil level.
- Excessive axial thrust (outlet pressure far exceeding the rated value), resulting in overloaded bearings.
- Large concentricity error during bearing installation, creating extra radial force during operation.
**Solutions**:
- Replace with lubricating oil matching the working conditions (extreme pressure anti‑wear type recommended), and keep the oil level at the center of the sight glass.
- Check the opening of the outlet pipeline valves and control the pressure within the rated range.
- Recalibrate the concentricity of the motor and pump shaft, with an error ≤ 0.05 mm.
### Coupling Vibration and Abnormal Noise
**Causes**:
- Aging or damage of the coupling elastic pad, leading to failure of cushioning.
- Misalignment between the pump shaft and motor shaft.
- Unbalanced dynamic balance of the screw rotor (caused by long‑term wear or impurities in the medium).
**Solutions**:
- Replace with an elastic pad of the same type, inspect and replace regularly (every 3000 hours).
- Correct the concentricity with a dial indicator.
- Disassemble the rotor for dynamic balance testing, and replace the rotor if severely worn.
## II. Medium Adaptation and Delivery Abnormalities
### Reduced Efficiency in High‑Viscosity Medium Delivery
**Causes**:
- Overly low screw speed, resulting in ineffective delivery of high‑viscosity medium.
- Overly low medium temperature, further increasing viscosity and internal friction resistance.
- Overly small inlet and outlet pipe diameters, causing excessive pipeline resistance.
**Solutions**:
- Increase the motor speed (verify whether the pump torque is sufficient).
- Apply heat tracing and insulation to the medium or pump body to reduce medium viscosity.
- Enlarge the inlet and outlet pipe diameters and reduce the number of elbows and valves.
### Gas Binding Caused by Gaseous Medium
**Causes**:
- Poor sealing of the suction pipeline, leading to air infiltration.
- Large amount of volatile components in the medium, vaporizing inside the pump.
- Incomplete priming, leaving air in the pump chamber.
**Solutions**:
- Check the sealing of suction pipeline flanges and connectors, and replace aged gaskets.
- Install a gas‑liquid separator before the pump inlet to separate gas before delivery.
- Ensure the vent valve is fully open during priming until no bubbles appear in the discharged medium.
### Wear Failure Caused by Solid Particles in the Medium
**Causes**:
- High hardness and large size of solid particles in the medium, causing erosion and wear on the screw meshing surfaces and pump liner.
- Lack of pre‑filtering device, allowing particles to enter the pump chamber directly.
**Solutions**:
- Install a basket filter at the pump inlet, with the filter mesh size ≤ 1/2 of the allowable particle diameter.
- Select screws made of wear‑resistant materials (such as duplex stainless steel, nitrided steel) and liners (such as polyurethane, ceramic).
## III. Advanced Seal System Problems
### Frequent Failure of Mechanical Seals
**Causes**:
- Insufficient flushing pressure in the seal chamber, failing to remove frictional heat.
- Particles in the medium scratching the seal faces.
- Improper compression amount during seal installation (too large / too small), resulting in poor contact of seal faces.
**Solutions**:
- Configure an independent flushing pipeline to ensure flushing pressure is 0.1–0.2 MPa higher than the medium pressure.
- Install a filtering device, or use a wear‑resistant seal face combination of cemented carbide + silicon carbide.
- Adjust the seal compression amount strictly according to the installation manual (usually 3–5 mm).
### Excessive Leakage of Packing Seals
**Causes**:
- Uneven tightening force of the packing gland, or aging and hardening of the packing.
- Grooves on the worn shaft sleeve, making the packing unable to seal.
- Overly high medium temperature, accelerating packing aging.
**Solutions**:
- Tighten the gland bolts evenly and step by step, avoiding one‑time over‑compression.
- Replace the worn shaft sleeve and use flexible graphite packing for high‑temperature media.
- Cool the packing chamber (install a cooling water jacket).
## IV. Installation and Operating Condition Matching Problems
### Cavitation Damage to the Pump Body
**Causes**:
- Excessively high suction height, resulting in inlet pressure lower than the saturated vapor pressure of the medium.
- Excessive resistance of the suction pipeline (small diameter, many elbows).
- Overly high medium temperature, increasing the saturated vapor pressure.
**Solutions**:
- Lower the pump installation height and adopt floodable installation.
- Optimize the suction pipeline design, shorten the pipeline length and enlarge the pipe diameter.
- Reduce the medium temperature or increase the inlet pressure.
### Uncoordinated Parallel / Series Operation
**Causes**:
- Inconsistent outlet pressures among multiple pumps in parallel, leading to uneven flow distribution.
- Insufficient inlet pressure of the downstream pump in series operation, causing cavitation.
**Solutions**:
- Use pumps of the same model and parameters for parallel operation, and install regulating valves at the outlet to balance pressure.
- During series operation, ensure the inlet pressure of the downstream pump is higher than the saturated vapor pressure of the medium; install a booster pump if necessary.
